Bryozoans 169 



Several Bryzoans secrete a gelatinous covering 

 instead of a solid tube, and the colonies become in- 

 vested in a soft transparent matrix. Pectinatella 

 (fig. 78) is one of these. It grows in large, more or 

 less spherical colonies, often resembling a muskmelon 

 in size, shape and superficial appearance. It is a not 

 uncommon inhabitant of bayous and ditches and slow- 

 flowing streams. It grows in most perfect spherical 

 form when attached to a rather small twig. The 

 clustered zooids form grayish rosettes upon the surface 

 of the huge translucent sphere. Late in the season 

 when statoblasts appear the surface becomes thickly 

 besprinkled with brown. Still later, after the zooids 

 have died, and the statoblasts have been scattered the 

 supporting gelatin persists, blocks and segments of 

 it, derived from disintegrating colonies, now green from 

 an overgrowth of algae, are scattered about the shores. 



There are but a few genera of fresh-water bryozoans 

 — some six or seven — and Plumatella is much the com- 

 monest one. Plumatella and allied forms grow in water 

 pipes. They gather in enormous masses upon the sluice- 

 ways and weirs of water reservoirs. They sometimes 

 cover every solid support with massive colonies of inter- 

 laced and heaped-up branches. Thus they form an 

 incrusting layer thick enough to be removed from flat 

 surfaces with shovels. Its removal is demanded because 

 the bryozoans threaten the potability of the water sup- 

 ply. They do no harm while living and active, but 

 when with unfavorable conditions they begin to die, 

 their decomposing remains may befoul the water of an 

 entire reservoir. 



Cristatella is a flat, rather leech-shaped form that is 

 often found on the under side of lily pads. It is re- 

 markable for the fact that the entire colony is capable 

 of a slow creeping locomotion.. The zooids act together 

 as one organism. 



